1. Technical Field
The disclosure relates to a liquid-sealed antivibration device.
2. Related Art
As an antivibration device such as an engine mount which supports a vibration source such as an automobile engine or the like while preventing the transmission of vibrations of the vibration source to a vehicle body side, there has been known a liquid-sealed antivibration device. The liquid-sealed antivibration device includes: a first mounting part which is mounted on the vehicle body side; a second mounting part which is mounted on a vibration source side; an antivibration base body which is interposed between the first mounting part and the second mounting part and is made of an elastomer; a main liquid chamber whose chamber wall is partially formed of the antivibration base body; a sub liquid chamber whose chamber wall is partially formed of a diaphragm; and an orifice flow passage which allows the main liquid chamber and the sub liquid chamber to communicate with each other.
In such a liquid-sealed antivibration device, when normal vibrations are inputted, due to a liquid column resonance action brought about by the flow of a liquid in an orifice flow passage or a vibration control effect of the antivibration base body, the liquid-sealed antivibration device performs a vibration damping function and a vibration insulating function. However, when large vibrations are inputted, the antivibration device per se becomes an abnormal sound generation source and there may be a case where an abnormal sound is transmitted in a cabin.
This abnormal sound is generated by cavitation in the liquid chamber. Cavitation is a phenomenon where when large vibrations are inputted to an antivibration device, an orifice flow passage is clogged so that the inside of a main liquid chamber is brought into an excessive negative pressure state (that is, a state where a liquid pressure in the main liquid chamber is lower than a predetermined value) and the pressure in the main liquid chamber becomes lower than a saturated vapor pressure of a sealed liquid thus generating a large number of bubbles. An impact sound which is generated when bubbles generated in this manner extinguish becomes an abnormal sound and is transmitted to the outside.
To prevent the generation of the abnormal sound caused by cavitation, for example, JP-A-2007-107712 discloses the constitution where a short-circuiting passage which short-circuits a main liquid chamber and a sub liquid chamber is formed in a partition member which partitions the main liquid chamber and the sub liquid chamber, and a valve element which switches the short-circuiting passage between a communication state and an interruption state is formed of a metal spring such as a plate spring whereby when the main liquid chamber is brought into an excessively negative pressure state, the short-circuiting passage is opened so that a liquid is supplied to the main liquid chamber from the sub liquid chamber. JP-A-2007-270866 also discloses the constitution where a valve element similar to the above-mentioned valve element is held by a spring.
JP-A-2008-175321 discloses the structure where a movable membrane is mounted on a partition element which partitions a main liquid chamber and a sub liquid chamber, a slit-like opening portion which functions as a valve element is formed in a portion of the movable membrane, and the valve element is arranged offset toward a sub liquid chamber side with respect to a valve element displacement restricting member thus imparting a function of a check valve.
The constitution disclosed in JP-A-2007-107712 adopts the structure where the metal spring and the partition member are brought into contact with each other by way of the valve element and hence, in returning the valve element to an original position after opening the valve, rigid bodies collide each other so that there exists a possibility that an abnormal sound is generated due to a large impact. Further, the metal spring is in an antifreeze liquid and hence, rust prevention treatment becomes necessary thus pushing up a cost. The constitution disclosed in JP-A-2007-270866 also adopts the structure where a valve element mainly made of metal which is directly connected with a spring is brought into contact with a partition member and hence, the constitution has a similar drawback.
On the other hand, in JP-A-2008-175321, there exists a possibility that a liquid always leaks from the slit formed in the valve element portion of the movable membrane and hence, the constitution has a drawback that a dumping performance by an orifice flow passage on the outer periphery which is to be originally exerted in a normal use region is lowered.